U.S. patent application number 16/976859 was filed with the patent office on 2021-01-07 for separator having no separator substrate.
This patent application is currently assigned to LG CHEM, LTD.. The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Kyoung Ho AHN, Young Duk KIM, Chul Haeng LEE, Je An LEE, Kwan Woo NAM.
Application Number | 20210005859 16/976859 |
Document ID | / |
Family ID | |
Filed Date | 2021-01-07 |
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United States Patent
Application |
20210005859 |
Kind Code |
A1 |
AHN; Kyoung Ho ; et
al. |
January 7, 2021 |
SEPARATOR HAVING NO SEPARATOR SUBSTRATE
Abstract
Disclosed herein is a porous separator for electrochemical
devices, configured to guarantee electrical insulation between a
positive electrode and a negative electrode, wherein the porous
separator includes no polyolefin substrate, and includes inorganic
particles, a binder for coupling between the inorganic particles,
and a crosslinking agent.
Inventors: |
AHN; Kyoung Ho; (Daejeon,
KR) ; NAM; Kwan Woo; (Daejeon, KR) ; LEE; Chul
Haeng; (Daejeon, KR) ; KIM; Young Duk;
(Daejeon, KR) ; LEE; Je An; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Assignee: |
LG CHEM, LTD.
Seoul
KR
|
Appl. No.: |
16/976859 |
Filed: |
April 17, 2019 |
PCT Filed: |
April 17, 2019 |
PCT NO: |
PCT/KR2019/004646 |
371 Date: |
August 31, 2020 |
Current U.S.
Class: |
1/1 |
International
Class: |
H01M 2/16 20060101
H01M002/16; C08K 3/22 20060101 C08K003/22 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2018 |
KR |
10-2018-0055138 |
Claims
1. A porous separator for electrochemical devices, which provides
electrical insulation between a positive electrode and a negative
electrode, wherein the porous separator comprises no polyolefin
substrate, and comprises a composition comprising inorganic
particles, a polymer binder for coupling between the inorganic
particles, and a crosslinking agent.
2. The porous separator according to claim 1, wherein the
crosslinking agent is represented by Chemical Formulas 1 to 5,
##STR00007## in Chemical Formulas 1 to 3, m is an integer of 1 to
100, n is an integer of 0 to 30, o is an integer of 1 to 1,000, and
a weight average molecular weight of Chemical Formulas 1 to 3 is
1,000 to 100,000, ##STR00008## in Chemical Formula 4, m4 is an
integer of 1 to 100, n4 is an integer of 0 to 30, o4 is an integer
of 1 to 1,000, a weight average molecular weight of Chemical
Formula 4 is 1,000 to 100,000, and p is a variable dependent
thereon, ##STR00009## in Chemical Formula 5, a and c are an integer
of 1 to 30, b is an integer of 1 to 1,000 and, a weight average
molecular weight is 1,000 to 100,000.
3. The porous separator according to claim 1, wherein the inorganic
particles include high-dielectric inorganic particles having a
dielectric constant of 1 or more, inorganic particles having
piezoelectricity, inorganic particles having lithium ion transfer
ability, alumina hydrate, or a mixture of two or more thereof.
4. The porous separator according to claim 2, wherein the inorganic
particles include at least one selected from the group consisting
of Al.sub.2O.sub.3, AlOOH, SiO.sub.2, MgO, TiO.sub.2 and
BaTiO.sub.2.
5. The porous separator according to claim 1, wherein the polymer
binder comprises at least one selected from the group consisting of
polyvinylidene fluoride, polyvinylidene
fluoride-hexafluoropropylene, polyvinylidene
fluoride-trichloroethylene, polyvinylidene
fluoride-chlorotrifluoroethylene, polymethyl methacrylate,
polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate,
ethylene vinyl acetate copolymer, polyethylene oxide, cellulose
acetate, cellulose acetate butyrate, cellulose acetate propionate,
cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl
cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose,
acrylonitrile butadiene styrene copolymer, ethylene-propylene-diene
terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR),
TFE, fluoro rubber, and polyimide.
6. The porous separator according to claim 5, wherein the polymer
binder comprises at least one selected from the group consisting of
polyvinylidene fluoride (PVdF), tetrafluoroethylene (TFE) and
polyimide.
7. The porous separator according to claim 1, wherein the porous
separator further comprises an initiator and/or a reaction
catalyst.
8. The porous separator according to claim 1, wherein a
crosslinking reaction temperature of the crosslinking agent is
120.degree. C. to 160.degree. C.
9. The porous separator according to claim 7, wherein the initiator
comprises an azo-based compound or a peroxide-based compound.
10. The porous separator according to claim 9, wherein the
azo-based compound comprises at least one selected from among
2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(isobutyronitrile),
2,2'-azobis(2,4-dimethylvaleronitrile), and
2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile).
11. The porous separator according to claim 9, wherein the
peroxide-based compound comprises at least one selected from among
tetramethylbutyl peroxyneodecanoate,
bis(4-butylcyclohexyl)peroxydicarbonate,
di(2-ethylhexyl)peroxydicarbonate, butyl peroxyneodecanoate,
dipropyl peroxydicarbonate, diisopropyl peroxydicarbonate,
diethoxyethyl peroxydicarbonate, diethoxyhexyl peroxydicarbonate,
hexyl peroxydicarbonate, dimethoxybutyl peroxydicarbonate,
bis(3-methoxy-3-methoxybutyl)peroxydicarbonate, dibutyl
peroxydicarbonate, dicetyl peroxydicarbonate, dimyristyl
peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxypivalate, hexyl
peroxypivalate, butyl peroxypivalate, trimethylhexanoyl peroxide,
dimethylhydroxybutyl peroxyneodecanoate, amyl peroxyneodecanoate,
Atofina, butyl peroxyneodecanoate, t-butyl peroxreoheptanoate, amyl
peroxypivalate, t-butyl peroxypivalate, t-amyl
peroxy-2-ethylhexanoate, lauroyl peroxide, dilauroyl peroxide,
didecanoyl peroxide, benzoyl peroxide, or dibenzoyl peroxide.
12. The porous separator according to claim 1, wherein the porous
separator has a thickness of 5 .mu.m to 30 .mu.m.
13. The porous separator according to claim 1, wherein a content of
the crosslinking agent is greater than 0 wt % and equal to or less
than 5 wt % of a total weight of a solid body in the porous
separator.
14. The porous separator according to claim 1, wherein the porous
separator has an air permeability of 50 sec/100 cc to 4,000 sec/100
cc.
15. An electrochemical device comprising the porous separator
according to claim 1.
Description
TECHNICAL FIELD
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 2018-0055138 filed on May 14, 2018,
the disclosure of which is hereby incorporated by reference herein
in its entirety.
[0002] The present invention relates to a separator having no
separator substrate, and more particularly to a separator that does
not include a polyolefin substrate, which is used as a separator
substrate, and includes inorganic particles, and a polymer binder
for coupling between the inorganic particles.
BACKGROUND ART
[0003] With the trends toward reducing the weight and increasing
the functionality of portable devices, such as smartphones, laptop
computers, tablet PCs, and portable game machines, the demand for a
secondary battery serving as a driving power source thereof is
increasing. In the past, nickel-cadmium, nickel-hydrogen, and
nickel-zinc batteries have been used, but lithium secondary
batteries, which have high operating voltage and high energy
density per unit weight, are most frequently used at present.
[0004] With the growth of markets related to the portable device
market, the demand for lithium secondary batteries has increased.
Lithium secondary batteries have also come to be used as the power
sources for electric vehicles (EV), hybrid electric vehicles (HEV)
and storage of renewable energy.
[0005] A lithium secondary battery is configured such that an
electrode assembly having a positive electrode/separator/negative
electrode structure, which can be charged and discharged, is
mounted in a battery case. Each of the positive electrode and the
negative electrode is manufactured by applying a slurry including
an electrode active material to one surface or both surfaces of a
metal current collector, drying the slurry, and rolling the metal
current collector having the dried slurry applied thereto.
[0006] The separator is one of the most important factors that
affect the performance and the lifespan of a secondary battery. It
is necessary for the separator to electrically isolate the positive
electrode and the negative electrode from each other and to exhibit
ion permeability and mechanical strength such that an electrolytic
solution can pass smoothly through the separator. As the
applications of high-energy lithium secondary batteries are
expanded, safety of the separator at high temperature is also
needed.
[0007] A separator including a separator substrate, which is
conventionally used, and an inorganic coating layer has a problem
in that the force of adhesion between the separator and an
electrode is not sufficient due to its material characteristics,
whereby the separator and the electrode are locally separated from
each other or wrinkles are formed at the interface between the
separator and the electrode, depending on the manufacturing
process. Polyolefin, which is generally used as the separator
substrate, has a problem with thermal stability in which polyolefin
melts at a high temperature.
[0008] In order to solve these problems, a separator including an
inorganic coating layer alone without a polyolefin separator
substrate has been proposed. However, the separator has a problem
in that the separator exhibits very low electrical insulation,
whereby the separator is vulnerable to a short circuit which occurs
in a battery when applying to an electrochemical device. In
addition, the separator is easily torn due to the low tensile force
and low elongation thereof. As a result, there is a fatal drawback
in that a micro-scale short circuit occurs in an electrode
assembly.
[0009] Patent Document 1 discloses a separator constituted by a
micro-porous polymer layer including organically reformed aluminum
boehmite and an organic polymer. However, this patent document does
not suggest a solution such as polymerization to increase the
strength of the separator.
[0010] Patent Document 2 relates to an electrolyte for lithium
batteries, a negative electrode including the electrolyte, and a
lithium battery, and discloses an intermediate layer comprising an
electrolyte and a solid electrolyte interposed between a positive
electrode and a negative electrode, wherein the intermediate layer
serves as a separator. This patent document has a structure
corresponding to the present invention in that the electrolyte is
interposed between the positive electrode and the negative
electrode or may include the separator. However, this patent
document is different from the present invention in that a
surface-modified nanoparticle composite is dispersed in a block
copolymer. In addition, Patent Document 2 only describes the effect
of surface modification of the nanoparticle.
[0011] Non-patent Document 1 discloses crosslinking of
PVdF-HFP/PEGDMA (polyethylene glycol dimethacrylate). In Non-patent
Document 1, however, the above-specified material is not applied to
the separator but is applied only to a polymer electrolytic
solution.
[0012] Non-patent Document 2 discloses a separator for lithium
secondary batteries, made of boehmite nanoparticles and
polyvinylidene fluoride polymer. However, it is noted that this
separator is not suitable for a high-stress battery cell assembly
process.
[0013] Non-patent Document 3 discloses a porous ceramic film based
on magnesium aluminate as a separator for lithium secondary
batteries exhibiting high flexibility and thermal stability.
However, this non-patent document does not disclose a method for
increasing the strength of the separator.
[0014] That is, an effective technology that is capable of
providing a separator having no polyolefin substrate, wherein the
separator exhibits high stability in a high-temperature
environment, high insulation, higher tensile strength and
elongation, excellent electrolytic impregnation characteristic, and
high ion transfer ability, thereby solving the above problems, has
not yet been suggested.
RELATED ART DOCUMENT
[0015] (Patent Document 1) U.S. Registered Patent No. 8883354
[0016] (Patent Document 2) Korean Patent Application Publication
No. 2016-0140211 [0017] (Non-patent Document 1) Thermal shutdown
behavior of PVdF-HFP-based polymer electrolytes comprising heat
sensitive cross linkable oligomers, J. Power Sources 144, 2005
[0018] (Non-patent Document 2) Boehmite-based ceramic separator for
lithium-ion batteries, Journal of Applied Electrochemistry, 2016,
69 [0019] (Non-patent Document 3) Thin, flexible and thermally
stable ceramic membranes as separator for lithium-ion batteries,
Journal of Membrane Science, 2014, 103
DISCLOSURE
Technical Problem
[0020] The present invention has been made in view of the above
problems, and it is an object of the present invention to provide a
technology that is capable of preventing the occurrence of a short
circuit in a battery due to damage to a separator and a separator
to which the technology is applied by using a separator including
no polyolefin substrate and having a structure including inorganic
particles and a binder for coupling between the inorganic
particles, thereby having high stability in a high temperature
environment, high insulation, excellent electrolyte impregnation
characteristic, high ion transfer ability and higher tensile
strength and elongation than a conventional separator while
guaranteeing insulation corresponding to the insulation of the
conventional separator.
Technical Solution
[0021] In accordance with an aspect of the present invention, the
above and other objects can be accomplished by the provision of a
porous separator for electrochemical devices configured to
guarantee electrical insulation between a positive electrode and a
negative electrode, wherein the porous separator may include no
polyolefin substrate and may be prepared by mixing a composition
for a separator comprising inorganic particles, a polymer binder
for coupling between the inorganic particles, and a crosslinking
agent, coating, drying and then crosslinking the crosslinking
agent, wherein a content of the crosslinking agent in the
composition is greater than 0 wt % and equal to or less than 5 wt %
of a total weight of a solid body in the porous separator.
[0022] The crosslinking agent may be represented by the following
Chemical Formulas.
##STR00001##
[0023] In Chemical Formulas 1 to 3, m is an integer of 1 to 100, n
is an integer of 0 to 30, and o is an integer of 1 to 1,000. A
weight average molecular weight of Chemical Formulas 1 to 3 is
1,000 to 100,000.
##STR00002##
[0024] In Chemical Formula 4, m4 is an integer of 1 to 100, n4 is
an integer of 0 to 30, and o4 is an integer of 1 to 1,000. A weight
average molecular weight of Chemical Formula 4 is 1,000 to 100,000
and p is a variable dependent thereon.
##STR00003##
[0025] In Chemical Formula 5, a and c are an integer of 1 to 30, b
is an integer of 1 to 1,000. A weight average molecular weight is
1,000 to 100,000.
[0026] The inorganic particles may be high-dielectric inorganic
particles having a dielectric constant of 1 or more, inorganic
particles having piezoelectricity, inorganic particles having
lithium ion transfer ability, alumina hydrate, or a mixture of two
or more thereof, preferably at least one selected from the group
consisting of Al.sub.2O.sub.3, AlOOH, SiO.sub.2, MgO, TiO.sub.2 and
BaTiO.sub.2.
[0027] The polymer binder may be at least one selected from the
group consisting of polyvinylidene fluoride, polyvinylidene
fluoride-hexafluoropropylene, polyvinylidene
fluoride-trichloroethylene, polyvinylidene
fluoride-chlorotrifluoroethylene, polymethyl methacrylate,
polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate,
ethylene vinyl acetate copolymer, polyethylene oxide, cellulose
acetate, cellulose acetate butyrate, cellulose acetate propionate,
cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl
cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose,
acrylonitrile butadiene styrene copolymer, ethylene-propylene-diene
terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR),
TFE, fluoro rubber, and polyimide. Preferably, the polymer binder
may be at least one selected from the group consisting of PVdF, TFE
and polyimide.
[0028] The porous separator may further comprise an initiator
and/or a reaction catalyst and the reaction temperature of the
crosslinking agent may be 120.degree. C. to 160.degree. C.
[0029] The initiator may be an azo-based compound or a
peroxide-based compound. For example, the azo-based compound may be
at least one selected from among
2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(isobutyronitrile),
2,2'-azobis(2,4-dimethylvaleronitrile), and
2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Preferably, the
azo-based compound may be 2,2'-azobis(isobutyronitrile).
[0030] The peroxide-based compound may be at least one selected
from among tetramethylbutyl peroxyneodecanoate,
bis(4-butylcyclohexyl)peroxydicarbonate,
di(2-ethylhexyl)peroxydicarbonate, butyl peroxyneodecanoate,
dipropyl peroxydicarbonate, diisopropyl peroxydicarbonate,
diethoxyethyl peroxydicarbonate, diethoxyhexyl peroxydicarbonate,
hexyl peroxydicarbonate, dimethoxybutyl peroxydicarbonate,
bis(3-methoxy-3-methoxybutyl)peroxydicarbonate, dibutyl
peroxydicarbonate, dicetyl peroxydicarbonate, dimyristyl
peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxypivalate, hexyl
peroxypivalate, butyl peroxypivalate, trimethylhexanoyl peroxide,
dimethylhydroxybutyl peroxyneodecanoate, amyl peroxyneodecanoate,
Atofina, butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate,
amyl peroxypivalate, t-butyl peroxypivalate, t-amyl
peroxy-2-ethylhexanoate, lauroyl peroxide, dilauroyl peroxide,
didecanoyl peroxide, benzoyl peroxide, and dibenzoyl peroxide.
[0031] It is desirable that the thickness of the porous separator
may range from 5 .mu.m to 30 .mu.m.
[0032] The content of the crosslinking agent may be greater than 2
wt % and equal to or less than 20 wt % of a total weight of a solid
body in the porous separator and the porous separator may have an
air permeability of 50 sec/100 cc to 4,000 sec/100 cc.
[0033] The present invention provides an electrochemical device
including a porous separator for electrochemical devices in
accordance with an aspect of the present invention.
BEST MODE
[0034] Now, the present invention will be described in detail with
reference to the accompanying drawings. It should be noted that
terms or words used in this specification and the claims are not to
be interpreted as having ordinary and dictionary-based meanings but
as having meanings and concepts coinciding with the technical idea
of the present invention based on the principle that the inventors
may properly define the concepts of the terms in order to explain
the invention in the best method. Consequently, the embodiments
described in this specification are merely the most preferred
embodiments and do not cover all technical ideas of the present
invention, and therefore it should be understood that there may be
various equivalents and modifications capable of substituting for
the embodiments at the time of filing of the present
application.
[0035] In accordance with an aspect of the present invention, there
is provided a porous separator for electrochemical devices
configured to guarantee electrical insulation between a positive
electrode and a negative electrode, wherein the porous separator
may include no polyolefin substrate and may include inorganic
particles, a polymer binder for coupling between the inorganic
particles, and a crosslinking agent.
[0036] Compared to a conventional separator, the porous separator
according to the present invention does not include a
polyolefin-based separator substrate. The conventional separator
includes a polyolefin-based separator substrate, to one surface of
which an inorganic layer including an inorganic material and a
binder is applied. In the present invention, however, the
conventional separator substrate is omitted, and the porous
separator is made of materials constituting an inorganic layer.
[0037] On the other hand, as another conventional separator, there
is a separator including an inorganic layer alone as a separator.
The overall strength of the conventional separator becomes low,
since the separator includes no polyolefin separator substrate. As
a result, the separator interposed between the electrode assemblies
may be damaged, whereby a short circuit may occur.
[0038] 1) Crosslinking Agent
[0039] The crosslinking agent may be represented by the following
Chemical Formulas.
##STR00004##
[0040] In Chemical Formulas 1 to 3, m is an integer of 1 to 100, n
is an integer of 0 to 30, and o is an integer of 1 to 1,000. A
weight average molecular weight of Chemical Formulas 1 to 3 is
1,000 to 100,000.
##STR00005##
[0041] In Chemical Formula 4, m4 is an integer of 1 to 100, n4 is
an integer of 0 to 30, and o4 is an integer of 1 to 1,000. A weight
average molecular weight of Chemical Formula 4 is 1,000 to 100,000
and p is a variable dependent thereon.
##STR00006##
[0042] In Chemical Formula 5, a and c are an integer of 1 to 30, b
is an integer of 1 to 1,000. A weight average molecular weight is
1,000 to 100,000.
[0043] The content of the crosslinking agent may be greater than 2
wt % and equal to or less than 20 wt %, preferably greater than 2
wt % and equal to or less than 10 wt o, more preferably greater
than 2 wt % and equal to or less than 8 wt %, much more preferably
greater than 3 wt % and equal to or less than 7 wt %, and most
preferably 4 wt % and equal to or less than 6 wt % of a total
weight of a solid body in the porous separator.
[0044] In the case in which the content of the crosslinking agent
is greater than the upper limit, crosslinking is not completely
performed. As a result, the crosslinking agent may serve locally as
a plasticizer, and therefore the tensile strength of the porous
separator is rather remarkably reduced, which is undesirable.
[0045] In the case in which the content of the crosslinking agent
is greater than 20 wt %, the ion conductivity of the porous
separator may become low due to a low content of inorganic
materials and the mechanical properties of the porous separator
such as thermal shrinkage may be deteriorated.
[0046] In the present invention, the crosslinking agent reacts at a
specific temperature to have a three-dimensional net-shaped
structure. The density of the porous separator is increased due to
the characteristics of the net-shaped structure, whereby the
physical properties, particularly the rigidity, are improved. The
electron migration is affected due to the characteristics of the
net-shaped structure, whereby the insulation resistance is
increased.
[0047] The reaction temperature of the crosslinking agent may be
120.degree. C. to 160.degree. C., preferably 130.degree. C. to
150.degree. C. The crosslinking agent, which has a linear structure
at temperatures lower than the above reaction temperature range,
reacts when the reaction temperature of the crosslinking agent
reaches the above reaction temperature range, whereby a
three-dimensional net-shaped structure is formed through
crosslinking.
[0048] In the case in which the reaction temperature of the
crosslinking agent is lower than 120.degree. C., the crosslink
joints of the crosslinking agent are not separated from each other,
whereby it is difficult for the crosslinking agent to perform a
crosslinking reaction, which is undesirable. In the case in which
the reaction temperature of the crosslinking agent is higher than
160.degree. C., the crosslinking agent or the binder used together
with the crosslinking agent may melt, which is also
undesirable.
[0049] In addition, since the porous separator according to the
present invention further includes a crosslinking agent in addition
to the inorganic particles and the binder, the porous separator may
have a high breakdown voltage even though the separator substrate
is omitted.
[0050] Specifically, in the case in which foreign matter, such as
iron (Fe), which is a conductive material, is applied to the porous
separator according to the present invention, it is confirmed that
the porous separator has a breakdown voltage value almost the same
as the breakdown voltage value of a separator including a separator
substrate that is used for a secondary battery for vehicles. In
addition, there is little difference between the breakdown voltage
of the porous separator before the conductive material is applied
and the breakdown voltage of the porous separator after the
conductive material is applied.
[0051] 2) Inorganic Particles
[0052] The inorganic particles may form empty spaces among the
inorganic particles, and thereby may form micro pores and maintain
a physical shape as a spacer. The physical characteristics of the
inorganic particles are not generally changed at a temperature of
200.degree. C. or more.
[0053] The inorganic particles are not particularly restricted, as
long as the inorganic particles are electrochemically stable. That
is, the inorganic particles that can be used in the present
invention are not particularly restricted as long as the inorganic
particles are not oxidized and/or reduced within the operating
voltage range (e.g. 0 to 5 V based on Li/Li+) of a battery to which
the inorganic particles are applied. Particularly, in the case in
which inorganic particles having high electrolyte ion transfer
ability are used, it is possible to improve the performance of an
electrochemical device. Consequently, it is preferable for the
electrolyte ion transfer ability of the inorganic particles to be
as high as possible. In addition, in the case in which the
inorganic particles have high density, it may be difficult to
disperse the inorganic particles at the time of forming the porous
separator, and the weight of a battery may increase at the time of
manufacturing the battery. For these reasons, it is preferable for
the density of the inorganic particles to be low. In addition, in
the case in which the inorganic particles have high permittivity,
the degree of dissociation of electrolyte salt, such as lithium
salt, in a liquid electrolyte may increase, thereby improving the
ion conductivity of the electrolytic solution.
[0054] For the reasons described above, the inorganic particles may
be high-dielectric inorganic particles having a dielectric constant
of 1 or more, preferably 10 or more, inorganic particles having
piezoelectricity, inorganic particles having lithium ion transfer
ability, alumina hydrate, or a mixture of two or more thereof.
[0055] Examples of the inorganic particles having a dielectric
constant of 1 or more may include SrTiO.sub.3, SnO.sub.2,
CeO.sub.2, MgO, NiO, CaO, ZnO, ZrO.sub.2, Y.sub.2O.sub.3,
Al.sub.2O.sub.3, TiO.sub.2, SiC, or a mixture thereof. However, the
present invention is not limited thereto.
[0056] The inorganic particles having piezoelectricity are a
material that is a nonconductor at normal pressure but, when a
certain pressure is applied thereto, exhibits conductivity due to a
change in the internal structure thereof. In the case in which the
inorganic particles have a high dielectric value, e.g. a dielectric
constant of 100 or more, and the inorganic particles are tensioned
or compressed with a certain pressure, electric charges are
generated. One face is charged as a positive pole and the other
face is charged as a negative pole, whereby a potential difference
is generated between the two faces.
[0057] In the case in which inorganic particles having the
above-mentioned characteristics are used, a short circuit may occur
in both electrodes in the event of an external impact, such as
local crushing or an impact with a nail. At this time, however, the
positive electrode and the negative electrode may not directly
contact each other due to the inorganic particles coated on the
porous separator, and potential differences in particles may occur
due to the piezoelectricity of the inorganic particles.
Accordingly, electron migration, namely, fine current flow, is
achieved between the two electrodes, whereby the voltage of the
battery is gradually reduced, and therefore the stability of the
battery may be improved.
[0058] Examples of the inorganic particles having piezoelectricity
may include BaTiO.sub.3, Pb(Zr,Ti)O.sub.3 (PZT),
Pb.sub.1-xLa.sub.xZr.sub.1-yTi.sub.yO.sub.3 (PLZT), Pb
(Mg.sub.1/3Nb.sub.2/3) O.sub.3--PbTiO.sub.3 (PMN-PT) hafnia
(HfO.sub.2), and a mixture thereof. However, the present invention
is not limited thereto.
[0059] The inorganic particles having lithium ion transfer ability
are inorganic particles that contain lithium elements and transport
lithium ions without storing lithium. The inorganic particles
having lithium ion transfer ability may transfer and transport
lithium ions due to a kind of defect present in a particle
structure. Consequently, lithium ionic conductivity in the battery
may be improved, and therefore the battery performance may be
improved.
[0060] Examples of the inorganic particles having lithium ion
transfer ability may include lithium phosphate (Li.sub.3PO.sub.4),
lithium titanium phosphate (Li.sub.xTi.sub.y(PO.sub.4).sub.3, where
0<x<2 and 0<y<3), lithium aluminum titanium phosphate
(Li.sub.xAl.sub.yTi.sub.z(PO.sub.4).sub.3, where 0<x<2,
0<y<1, and 0<z<3), (LiAlTiP).sub.xO.sub.y-based glass
(where 0<x<4 and 0<y<13) such as
14Li.sub.2O-9Al.sub.2O.sub.3-38TiO.sub.2-39P.sub.2O.sub.5, lithium
lanthanum titanate (Li.sub.xLa.sub.yTiO.sub.3, where 0<x<2
and 0<y<3), lithium germanium thiophosphate
(Li.sub.xGe.sub.yP.sub.zS.sub.w, where 0<x<4, 0<y<1,
0<z<1, and 0<w<5) such as
Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4, lithium nitride
(Li.sub.xN.sub.y, where 0<x<4 and 0<y<2) such as
Li.sub.3N, SiS.sub.2-based glass (Li.sub.xSi.sub.yS.sub.z where
0<x<3, 0<y<2, and 0<z<4) such as
Li.sub.3PO.sub.4--Li.sub.2S--SiS.sub.2, P.sub.2S.sub.5-based glass
(Li.sub.XP.sub.YS.sub.Z, where 0<x<3, 0<y<3, and
0<z<7) such as LiI--Li.sub.2S--P.sub.2S.sub.5, and a mixture
thereof. However, the present invention is not limited thereto.
[0061] The alumina hydrate may be classified as crystalline alumina
hydrate or gel-type alumina hydrate depending on the method of
manufacturing the same. Examples of the crystalline alumina hydrate
may include gibbsite .sub.i-Al(OH).sub.3, bayerite Al(OH).sub.3,
diaspore .sub.i-AlOOH, and boehmite .sub.i-AlOOH, and the gel-type
alumina hydrate may be aluminum hydroxide, which is prepared by
depositing an aqueous solution containing aluminum ions using
ammonia. Preferably, boehmite .sub.i-AlOOH may be used as the
gel-type alumina hydrate.
[0062] In the case in which the inorganic particles having high
permittivity, the inorganic particles having piezoelectricity, the
inorganic particles having lithium ion transfer ability, and the
alumina hydrate are used together, the effects obtained through
these ingredients may be further improved.
[0063] The size of each of the inorganic particles is not
particularly restricted. In order to form a film having a uniform
thickness and to achieve appropriate porosity, however, each of the
inorganic particles may have a size of 0.001 .mu.m to 10 .mu.m. In
the case in which the size of each of the inorganic particles is
less than 0.001 .mu.m, dispersibility is reduced, whereby it is
difficult to adjust the physical properties of the porous
separator. In the case in which the size of each of the inorganic
particles is greater than 10 .mu.m, the thickness of a separator
manufactured with the same content of a solid body is increased,
whereby the mechanical properties of the separator are
deteriorated. In addition, a short circuit may easily occur in the
battery when the battery is charged and discharged due to
excessively large-sized pores.
[0064] 3) Polymer Binder
[0065] The polymer binder may become a gel when the polymer binder
is impregnated with a liquid electrolytic solution, whereby the
polymer binder may have a characteristic of exhibiting high rate of
electrolytic solution impregnation. In fact, in the case in which
the polymer binder is a polymer having a high rate of electrolytic
solution impregnation, an electrolytic solution injected after the
assembly of a battery permeates into the polymer, and the polymer
impregnated with the electrolytic solution exhibits electrolyte ion
transfer ability. In addition, compared to a conventional
hydrophobic polyolefin-based separator, wetting of the porous
separator in the electrolytic solution may be improved, and it is
possible to use polar electrolytic solutions for batteries, which
has been difficult conventionally. Consequently, the polymer binder
may have a polymer with solubility parameter of 15 MPa.sup.1/2 to
45 MPa.sup.1/2, preferably 15 MPa.sup.1/2 to 25 MPa.sup.1/2 and 30
MPa.sup.1/2 to 45 MPa.sup.1/2. In the case in which the solubility
parameter of the polymer binder is less than 15 MPa.sup.1/2 and
greater than 45 MPa.sup.1/2, it is difficult to impregnate the
polymer binder with a general electrolytic solution for
batteries.
[0066] Specifically, the polymer binder may be at least one
selected from the group consisting of polyvinylidene fluoride,
polyvinylidene fluoride-hexafluoropropylene, polyvinylidene
fluoride-trichloroethylene, polyvinylidene
fluoride-chlorotrifluoroethylene, polymethyl methacrylate,
polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate,
ethylene vinyl acetate copolymer, polyethylene oxide, cellulose
acetate, cellulose acetate butyrate, cellulose acetate propionate,
cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl
cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose,
acrylonitrile butadiene styrene copolymer, ethylene-propylene-diene
terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR),
TFE, fluoro rubber, and polyimide. Preferably, the polymer binder
may be at least one selected from the group consisting of PVdF, TFE
and polyimide.
[0067] 4) Initiator and Reaction Catalyst
[0068] The porous separator may further include an initiator for
reaction with the crosslinking agent in order to improve the
physical properties of the porous separator through the
crosslinking reaction.
[0069] The initiator may be an azo-based compound or a
peroxide-based compound. Specifically, the azo-based compound may
be at least one selected from among
2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(isobutyronitrile),
2,2'-azobis(2,4-dimethylvaleronitrile), and
2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Preferably, the
azo-based compound is 2,2'-azobis(isobutyronitrile).
[0070] The peroxide-based compound may be at least one selected
from among tetramethylbutyl peroxyneodecanoate,
bis(4-butylcyclohexyl)peroxydicarbonate,
di(2-ethylhexyl)peroxydicarbonate, butyl peroxyneodecanoate,
dipropyl peroxydicarbonate, diisopropyl peroxydicarbonate,
diethoxyethyl peroxydicarbonate, diethoxyhexyl peroxydicarbonate,
hexyl peroxydicarbonate, dimethoxybutyl peroxydicarbonate,
bis(3-methoxy-3-methoxybutyl)peroxydicarbonate, dibutyl
peroxydicarbonate, dicetyl peroxydicarbonate, dimyristyl
peroxydicarbonate, 1,1,3,3-tetramethylbutyl peroxypivalate, hexyl
peroxypivalate, butyl peroxypivalate, trimethylhexanoyl peroxide,
dimethylhydroxybutyl peroxyneodecanoate, amyl peroxyneodecanoate,
Atofina, butyl peroxyneodecanoate, t-butyl peroxyneoheptanoate,
amyl peroxypivalate, t-butyl peroxypivalate, t-amyl
peroxy-2-ethylhexanoate, lauroyl peroxide, dilauroyl peroxide,
didecanoyl peroxide, benzoyl peroxide, and dibenzoyl peroxide.
[0071] 5) Characteristics of Separator
[0072] Compared to a conventional separator, the porous separator
according to the present invention is configured to have a
structure including no separator substrate, whereby the strength of
the porous separator may be low. For this reason, the porous
separator may have a relatively large thickness. The thickness of
the porous separator may range from 5 .mu.m to 30 .mu.m.
[0073] In the case in which the thickness of the porous separator
is less than 5 .mu.m, the strength of the porous separator is low,
whereby the porous separator may be easily damaged, which is
undesirable. In the case in which the thickness of the porous
separator is greater than 30 .mu.m, the overall thickness of the
electrode assembly is increased, whereby the capacity of the
battery may be reduced, which is also undesirable.
[0074] The porous separator may have an air permeability of 50
sec/100 cc to 4,000 sec/100 cc. In the case in which the air
permeability of the porous separator is less than 50 sec/100 cc,
the insulation property of the porous separator is very low, which
is undesirable. In the case in which the air permeability of the
porous separator is greater than 4,000 sec/100 cc, the impregnation
of the porous separator with the electrolytic solution and the ion
conductivity of the separator become low, which is also
undesirable.
[0075] The physical properties of the porous separator are affected
by the reaction temperature and the reaction time. As the reaction
temperature and the reaction time are increased, the extent of
crosslinking is increased.
[0076] 6) Construction and Application of Electrode Assembly
[0077] The present invention also provides an electrochemical
device including a positive electrode, a negative electrode, the
porous separator interposed between the positive electrode and the
negative electrode, and an electrolyte. Here, the electrochemical
device may be a lithium secondary battery.
[0078] The positive electrode may be manufactured by applying a
mixture of a positive electrode active material, a conductive
agent, and a binder to a positive electrode current collector and
drying the mixture. A filler may be further added to the mixture as
needed.
[0079] In general, the positive electrode current collector is
manufactured so as to have a thickness of 3 to 500 .mu.m. The
positive electrode current collector is not particularly
restricted, as long as the positive electrode current collector
exhibits high conductivity while the positive electrode current
collector does not induce any chemical change in a battery to which
the positive electrode current collector is applied. For example,
the positive electrode current collector may be made of stainless
steel, aluminum, nickel, titanium, or plastic carbon.
Alternatively, the positive electrode current collector may be made
of aluminum or stainless steel, the surface of which is treated
with carbon, nickel, titanium, or silver. In addition, the positive
electrode current collector may have a micro-scale uneven pattern
formed on the surface thereof so as to increase the force of
adhesion of the positive electrode active material. The positive
electrode current collector may be configured in various forms,
such as those of a film, a sheet, a foil, a net, a porous body, a
foam body, and a non-woven fabric body.
[0080] The positive electrode active material may be, but is not
limited to, a layered compound, such as a lithium cobalt oxide
(LiCoO.sub.2) or a lithium nickel oxide (LiNiO.sub.2), or a
compound substituted with one or more transition metals; a lithium
manganese oxide represented by the chemical formula
Li.sub.1+xMn.sub.2-xO.sub.4 (where x=0 to 0.33) or a lithium
manganese oxide, such as LiMnO.sub.3, LiMn.sub.2O.sub.3, or
LiMnO.sub.2; a lithium copper oxide (Li.sub.2CuO.sub.2); a vanadium
oxide, such as LiV.sub.3O.sub.8, V.sub.2O.sub.5, or
Cu.sub.2V.sub.2O.sub.7; an Ni-sited lithium nickel oxide
represented by the chemical formula LiNi.sub.1-xM.sub.xO.sub.2
(where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3); a
lithium manganese composite oxide represented by the chemical
formula LiMn.sub.2-xM.sub.xO.sub.2 (where M=Co, Ni, Fe, Cr, Zn, or
Ta, and x=0.01 to 0.1) or the chemical formula
Li.sub.2Mn.sub.3MO.sub.8 (where M=Fe, Co, Ni, Cu, or Zn);
LiMn.sub.2O.sub.4 having Li of a chemical formula partially
replaced by alkaline earth metal ions; a disulfide compound; or
Fe.sub.2(MoO.sub.4).sub.3.
[0081] The conductive agent is generally added so that the
conductive agent accounts for 1 to 30 wt % based on the total
weight of the compound including the positive electrode active
material. The conductive agent is not particularly restricted, as
long as the conductive agent exhibits high conductivity without
inducing any chemical change in a battery to which the conductive
agent is applied. For example, graphite, such as natural graphite
or artificial graphite; carbon black, such as carbon black,
acetylene black, Ketjen black, channel black, furnace black, lamp
black, or summer black; conductive fiber, such as carbon fiber or
metallic fiber; metallic powder, such as carbon fluoride powder,
aluminum powder, or nickel powder; conductive whisker, such as a
zinc oxide or potassium titanate; a conductive metal oxide, such as
a titanium oxide; or conductive materials, such as polyphenylene
derivatives, may be used as the conductive agent.
[0082] The binder is a component assisting in binding between the
active material and the conductive agent and in binding with the
current collector. The binder is generally added in an amount of 1
to 30 wt % based on the total weight of the compound including the
positive electrode active material. As examples of the binder,
there may be used polyvinylidene fluoride, polyvinyl alcohol,
carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,
regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene,
polyethylene, polypropylene, ethylene-propylene-diene terpolymer
(EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber,
and various copolymers.
[0083] The filler is an optional component used to inhibit
expansion of the positive electrode. There is no particular limit
to the filler, as long as it does not cause chemical changes in a
battery to which the filler is applied and is made of a fibrous
material. As examples of the filler, there may be used olefin
polymers, such as polyethylene and polypropylene; and fibrous
materials, such as glass fiber and carbon fiber.
[0084] The negative electrode may be manufactured by applying a
negative electrode material to a negative electrode current
collector and drying the same. The above-described components may
be selectively further included as needed.
[0085] In general, the negative electrode current collector is
manufactured so as to have a thickness of 3 .mu.m to 500 .mu.m. The
negative electrode current collector is not particularly
restricted, as long as the negative electrode current collector
exhibits high conductivity while the negative electrode current
collector does not induce any chemical change in a battery to which
the negative electrode current collector is applied. For example,
the negative electrode current collector may be made of copper,
stainless steel, aluminum, nickel, titanium, or plastic carbon.
Alternatively, the negative electrode current collector may be made
of copper or stainless steel, the surface of which is treated with
carbon, nickel, titanium, or silver, or an aluminum-cadmium alloy.
In addition, the negative electrode current collector may have a
micro-scale uneven pattern formed on the surface thereof so as to
increase the force of adhesion of the negative electrode active
material, in the same manner as the positive electrode current
collector. The negative electrode current collector may be
configured in various forms, such as those of a film, a sheet, a
foil, a net, a porous body, a foam body, and a non-woven fabric
body.
[0086] As the negative electrode active material, for example,
there may be used carbon, such as a hard carbon or a graphite-based
carbon; a metal composite oxide, such as Li.sub.xFe.sub.2O.sub.3
(0.ltoreq.x.ltoreq.1), Li.sub.xWO.sub.2 (0.ltoreq.x.ltoreq.1),
Sn.sub.xMe.sub.1-xMe'.sub.yO, (Me: Mn, Fe, Pb, Ge; Me': Al, B, P,
Si, Group 1, 2 and 3 elements of the periodic table, halogen;
0<x.ltoreq.1; 1.ltoreq.y.ltoreq.3; 1.ltoreq.z.ltoreq.8); lithium
metal; lithium alloy; silicon-based alloy; tin-based alloy; a metal
oxide, such as SnO, SnO.sub.2, PbO, PbO.sub.2, Pb.sub.2O.sub.3,
Pb.sub.3O.sub.4, Sb.sub.2O.sub.3, Sb.sub.2O.sub.4, Sb.sub.2O.sub.5,
GeO, GeO.sub.2, Bi.sub.2O.sub.3, Bi.sub.2O.sub.4, or
Bi.sub.2O.sub.5; a conductive polymer, such as polyacetylene; or a
Li--Co--Ni based material.
[0087] In accordance with another aspect of the present invention,
there is provided a battery pack including the electrochemical
device.
[0088] Specifically, the battery pack may be used as a power source
for a device requiring the ability to withstand high temperatures,
a long lifespan, high rate characteristics, etc. Specific examples
of the device may include a mobile electronic device, a wearable
electronic device, a power tool driven by a battery-powered motor;
an electric automobile, such as an electric vehicle (EV), a hybrid
electric vehicle (HEV), or a plug-in hybrid electric vehicle
(PHEV); an electric two-wheeled vehicle, such as an electric
bicycle (E-bike) or an electric scooter (E-scooter); an electric
golf cart; and a power storage system. However, the present
invention is not limited thereto.
[0089] The structure and manufacturing method of the device are
well known in the art to which the present invention pertains, and
a detailed description thereof will be omitted.
EXAMPLE
[0090] Hereinafter, the present invention will be described in
detail with reference to the following Examples and Experimental
Example; however, the present invention is not limited by the
Examples and the Experimental Example. The Examples may be modified
into various other forms, and the scope of the present invention
should not be interpreted as being limited by the Examples, which
will be described in detail. The Examples are provided in order to
more completely explain the prevent invention to a person who has
average knowledge in the art to which the present invention
pertains.
Example 1
[0091] A slurry was manufactured such that the content of a solid
body including boehmite (AlO(OH)), as inorganic particles,
polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP,
5130), as a binder, and a compound represented by Chemical Formula
4, as a crosslinking agent, mixed in a ratio of 78:20:2, became 18
wt % of the total weight of the slurry.
[0092] Specifically, 28.08 g of boehmite (AlO(OH)), 7.2 g of
PVdF-HFP, and 0.72 g of the compound represented by Chemical
Formula 4 were added to 164 g of acetone in order to manufacture a
slurry. The slurry was formed so as to have the shape of a
separator and then dried at 150.degree. C. for 30 minutes in order
to manufacture a separator. After the crosslinking reaction, the
separator was further dried at ambient temperature in order to
complete the separator.
Example 2
[0093] A separator was manufactured using the same method as in
Example 1, except that 0.0072 g of 2,2'-azobis(isobutyronitrile),
as an initiator, was added to the slurry manufactured according to
Example 1.
Example 3
[0094] A separator was manufactured using the same method as in
Example 1, except that a compound represented by Chemical Formula 5
was used in place of the compound represented by Chemical Formula 4
in the slurry of Example 1.
Example 4
[0095] A separator was manufactured using the same method as in
Example 2, except that the compound represented by Chemical Formula
5 was used in place of the compound represented by Chemical Formula
4 in the slurry of Example 2.
Comparative Example 1
[0096] A separator was manufactured using the same method as in
Example 1, except that a solid body including boehmite (AlO(OH))
and polyvinylidene fluoride-hexafluoropropylene copolymer
(PVdF-HFP, 5130), mixed at a ratio of 78:22, was used without the
compound represented by Chemical Formula 4 and the compound
represented by Chemical Formula 5, as crosslinking agents.
Experimental Example 1
[0097] The volumetric resistivity, the electrical resistance, the
tensile strength, the swelling, the air permeability, and the
thickness of the separators according to Example 1, Example 2,
Example 3, Example 4, and Comparative Example 1 were measured.
TABLE-US-00001 TABLE 1 Volumetric Tensile Air resistivity
Resistance strength Swelling permeability Experiment Crosslinking
agent Initiator {T.OMEGA.*cm] [.OMEGA.] [kg/cm2] [%] [sec/100 cc]
Example 1 Chemical Formula 4 2% X 150 1.80 145 4.5 1010 Example 2
Chemical Formula 4 2% .largecircle. 161.5 1.75 170 2.0 1022 Example
3 Chemical Formula 5 2% X 77 1.95 150 5.0 1280 Example 4 Chemical
Formula 5 2% .largecircle. 78.7 1.85 179 2.3 1226 Comparative -- --
76.9 1.75 151 3.5 1706 Example 1
INDUSTRIAL APPLICABILITY
[0098] As is apparent from the above description, a porous
separator for electrochemical devices according to the present
invention does not include a polyolefin substrate, which is used as
a separator substrate of a conventional separator, and is made of a
material including inorganic particles, a binder, and a
crosslinking agent. Consequently, it is possible to solve a problem
in which the thermal stability of the separator substrate is low.
Furthermore, the crosslinking agent compound forms a
three-dimensional net-shaped structure, whereby it is possible to
remarkably improve the insulation of the separator.
[0099] In addition, since the crosslinking agent is changed from a
linear structure to a three-dimensional net-shaped structure, the
tensile strength and elongation of the separator are improved,
whereby the likelihood of damage to the separator is reduced.
Consequently, it is possible to prevent a short circuit in a
battery.
[0100] In addition, it is advantageous in that it has high
stability in a high temperature environment, excellent electrolyte
impregnation characteristic, and high ion transfer ability.
* * * * *